Module 1: Wireless Sensor Networks

Transcription

1 Module 1: Wireless Sensor Networks Dr. Ing. Koojana Kuladinithi, TZI, University of Bremen

2 Contents Module I Introduction to WSNs (Wireless Sensor Networks) IETF Standards for WSNs 6LOWPAN (IPv6 over Low power WPAN): IP Adaptation Layer ROLL (Routing Over Low power and Lossy networks): IP routing CORE/CoAP (Constrained RESTful Environments/Constrained Application Protocol): Application IPv6 Protocol 6LoWPAN Adaptation Layer Header compression Optimized neighbor discovery protocols Fragmentation 2

3 Sensor Node Introduction to WSN Limited in energy, computational power, storage capacity, transmission range & data rate TelosB TelosB mote: MSP430 microcontroller with 10kB RAM 16-bit RISC with 48K Program Flash IEEE compliant radio (< 250 kbps) 1MB external data flash Runs TinyOS or higher Two AA batteries/usb 1.8 ma (active); 5.1uA (sleep) UC Berkeley: Smart Dust Temperature, humidity, pressure, light, orientation, vibration, gas, etc WSN: Wireless Sensor Networks A collection of embedded tiny devices (sensors) with networking capabilities 3

4 WSNs / Wireless Embedded Internet Core Internet (Million nodes) Fringe Internet (Billion nodes) Using the Internet in very low power devices Consists of embedded, low power devices connected to the Internet (sensors, machines, RFIDs, etc) Also called as embedded fringe Image Source: 4

5 WSN: Architecture 5

6 A Single Node vs Wireless Sensor Network Extended range of sensing: Cover a wider area Extended functionality: Sensor nodes can not only perform sensing functionality, but also provide forwarding service Redundancy: Multiple nodes close to each other increase fault tolerance 6

7 WSN Applications Home and building automation The use of sensors and control to improve the operations and efficiency of a building Industrial automation Real time environmental monitoring and forecasting Logistic Tracking Use of active tags on people, equipment and supplies. Tracking results are used in asset management Smart metering The use of electricity, gas, water can be reduced and better controlled through more intelligent metering (use of intelligent lighting control, HVAC heating, ventilation and air conditioning control) 7

8 Evolution of Wireless Sensor Networks Price Scalability Cabling Proprietary radio + network ZigBee 6lowpan Internet Any vendor Z-Wave, prop. ISM etc. ZigBee and WHART 6lowpan ISA100 Cables Vendor lock-in Complex middleware Open development and portability 1980s > Image Source: Increased Productivity 8

9 Relationship of Standards Image Source: IETF: Internet Engineering Task Force CORE: Constrained RESTful Environments ROLL: Routing Over Low power Lossy networks 6LOWPAN: IPv6 over Lower power Wireless PAN IPSO: IP for Smart Object OGC: Open Geospatial Consortium ETSI: European Telecommunications Standards Institute ISA: Industrial Standardisation for Automation 9

10 Why IP based? Allows the use of existing network infrastructure IP based devices can be connected easily to other IP networks IP-based technologies have existed for decades (very well known, have been proven to work and scale) IP technology is specified in an open and free way Tools for managing, commissioning and diagnosing already exist Issues Bandwidth and frame size (e.g. IPv6 frame size 1280 bytes, IEEE frame size 127 bytes) - Web services (HTTP, SOAP & XML) Power and duty cycle - assumption of IP is that a device is always connected Reliability - e.g. TCP is not able to differentiate between packets dropped because of congestion or a packets lost on wireless links) 10

11 Introduction to IPv6 11

12 IPv4 vs IPv6 Addressing 128-bit IPv6 address = 64-bit prefix + 64-bit Interface ID (IID) Image source: Indeterminant (Wikipeida) 128-bit IPv6 address : each 16 bit values (four hex digits) separated by colons, one sequence of all-zero 16- bit values can be replaced by a double colon indicating a longer sequence of zeros 12

13 IPv6 Address Configuration 64-bit network Prefix 64-bit Suffix / Interface Identifier (IID) Stateless Address Auto Configuration EUI 64-bit IEEE 15.4 short addresses Stateful Address Configuration DHCPv6 13

14 IPv6 Address: 64 bit IID 64-bit IEEE EUI-64 bit (Extended Unique Identifier) 24-bit OUI (Organizationally Unique Identifier) 40-bit of extension identifier decided by the manufacturer OUI L M OUI (Cont.) Extension identifier Example: MAC address: 00:1D:BA:06:37:64 converts to 64-bit EUI address IID: 00:1D:BA:FF:FE:06:37:64 - Based on MAC address Network Prefix: 2001:db8:1:2::/64 Full IPv6 Address : 2001:db8:1:2:021D:BAFF:FE06:3764 Appendix A RFC 4291: IP Version 6 Addressing Architecture 14

15 IPv6 Address: 64 bit IID, Cont. 64-bit IID based on 15.4 short address PAN ID 0 PAN ID (cont) 0 0 F F F E bit short address 15

16 IPv6 Addresses in Hexadecimal Notation Long form Abbreviated form Explanation 2001:DB8:0.0:8:800:200C.417A 2001:DB8::8:800:200C:417A A unicast address FF01:0:0:0:0:0:0:101 FF01::101 A multicast address 0:0:0:0:0:0:0:1 ::1 Loopback address FE80:0:0:0: FE80:: A Link Local address 16

17 IPv6 Neighbor Discovery RFC 4861 ND: How hosts and routers interact with each other on the same link IPv6 is the format - ND is the brain One-hop routing protocol defined in RFC4861 Finding Routers Router Solicitation / Router Advertisement Finding Neighbors Neighbor Solicitation / Neighbor Acknowledgement Detecting Duplicate Addresses using NS/NA Address resolution using NS/NA Neighbor Unreachability Detection using NS/NA Image Source: ND: Neighbor Discovery NS: Neighbor Solicitation NA: Neighbor Advertisement DAD: Duplicate Address Detection 17

18 IPv6 Header Version Traffic Class Flow Label Payload Length Next Header Hop Limit bits: DSCP (Differentiated Services Control Point), group traffic to different classes 2 bits: Explicit Congestion Notification (ECN) RFC Source Address The extension header mechanism provides extensibility to support future services for security, mobility, and others, without redesign of the basic protocol Destination Address The packet header in IPv6 is simpler than that used in IPv4. IPv6 routers do not perform fragmentation The IPv6 header is not protected by a checksum. IPv6 routers do not need to recompute a checksum when header fields (such as the hop limit change) The TTL field of IPv4 has been renamed to Hop Limit 18

19 Introduction to 6LOWPAN 19

20 FC DSN DSTPAN DST SRC MAC Payload FCS FC DSN DSTPAN DST SRCPAN SRC Security MAC Payload FCS MAC Frame Num of bytes: 2 1 0/2 2/8 0/2 2/8 0/5/6/10/14 variable bytes MAX MAC frame with 64 bit addresses (without any security option) 104 bytes 21 B 2 B 20

21 IP over Header overhead Standard IPv6 header is 40 bytes [RFC 2460] Entire MTU is 127 bytes Fragmentation IPv6 requires all links support 1280 byte packets [RFC 2460] A full IPv6 packet does not fit into frame size Transport header Application payload 40 B + options IP header 1280 Bytes net payload MAC header 127 Bytes MAX? link payload FCS 21

22 What is 6LoWPAN? 6LoWPAN : IPv6 over Low-power Wireless Personal Area Networks Defined by IETF standards (draft-ietf-6lowpan-hc) RFC 4944 RFC 6282 Header compression Stateless Context based Neighbor discovery draft-ietf-6lowpan-nd (RFC 6775) Minimal use of code and memory Direct end-to-end Internet integration IPv6 Image Source: 22

23 Protocol Stack Low power wireless technologies Image Source: 23

24 6LoWPAN Architecture LoWPANs are stub networks Nodes (Host/Router) Simple LoWPAN A collection of nodes which shares a common IPv6 address prefix Single Edge Router (handles compressions & ND, IPv4 interconnectivity) Extended LoWPAN Multiple Edge Routers with common backbone link Ad-hoc LoWPAN Not connected to the Internet Image Source: ND: Neighbor Discovery R: Routers, H: Host 24

25 WSNs: Addressing IPv6 addresses are typically formed using Network Prefix: Prefix of the LoWPAN IID: Link Layer address of the wireless interface (64bit EUI / 16 bit short address) Flat LL addressing for all the devices Support unique long addresses (EUI-64) Configurable short addresses (usually 8-16 bits in length) Also support broadcast (0xFFFF in IEEE ), but do not support native multicast 25

26 Addressing : Example 6LoWPAN Assumption: LoWPAN uses IEEE and IP routing Edge Router Configures IPv6 prefix to its wireless interface (2001:300a:1::/48) Advertizes IPv6 prefix to nodes in the LoWPAN LoWPAN node IPv6 address with a 64-bit IID Receives generated IPv6 address with a 16 bit IID (HOST :: 1 -> 2001:300a:1::1) Routing Packets sent within LoWPAN do not require to have IPv6 network prefix inline Packets destined outside LoWPAN -> require to have IPv6 address inline Image Source: 26

27 SN 6LoWPAN: IP Header Compression Network IP Packet V TC FL L NH HL 8 B Src IP Dest IP 16 B 16 B net payload Link Packet FC PAN net payload DST SRC HL FCS 3 B 2 Bytes of 6LoWPAN adaptation headers ( dispatch + HC1) Eliminate all fields in the IPv6 header that can be derived from the header Version (V) : always v6 and no need to be sent Traffic Class (TC) & Flow Label (FL) : zero Length (L) : derived from link frame length Next Header (NH) : UDP, TCP, or ICMP Source address (Src IP) : derived from link address Destination address (Dest IP) : derived from link address 27

28 Compressed IPv6 Header v6 zeros Version Traffic Class Flow Label In header Payload Length Next Header Hop Limit Source Address IPv6 address derive from header derive from header + Destination Address + Interface identifier generated from EUID64 or Pan ID & short address + + Hop Limit is the only incompressible IPv6 header field Uncompressed 28

29 LoWPAN Dispatch Header Dispatch : To understand what is coming Typ Value type-specific header Dispatch 00 Not a LoWPAN headdr 01 LoWPAN IPv6 addressing header 10 LoWPAN Mesh header 11 LoWPAN Fragmentation Header How it is compressed: HC1, HC IPv6 Uncompressed IPv6 Addresses LOWPAN_HC1 - LOWPAN_HC1 compressed IPv LOWPAN_BC0 - LOWPAN_BC0 broadcast

30 6LoWPAN Dispatch Header 30

31 HC1 : Stateless Header Compression LOWPAN_HC1 compressed IPv6 Source Address Encoding Destination Address Encoding 00 Prefix sent in-line, IID sent in-line 01 Prefix sent in-line, IID derived from L2 10 Prefix = link local, IID sent in-line 11 Prefix = link local, IID derived from L SAE DAE C NH HC1 Traffic and Flow Label zero (compressed) Next Header Field 00 uncompressed, 01 UDP, 10 TCP, 11 ICMP Additional HC2 compression header follows Zero or more uncompressed fields follow in order Typ Value type-specific header Dispatch 31

32 HC2: Stateless Header Compression Source Port Destination Port Length Checksum UDP Payload UDP Port numbers : UDP: HC2-8 bytes header is compressed to 3 bytes source port = P + 4 bits, where p = (0xF0B0) destination port = P + 4 bits Length = (Payload of IPv6 header - length of any extension headers present between the IPv6 header and the UDP header) S_Port D_Port Checksum 32

33 HC2 : Stateless Header Compression Source Port is compressed Destination Port is compressed Length is compressed SAE DAE C NH S D L uncompressed fields follow in order Dispatch (LowPAN IPv6 HC1) HC1 HC2 3 bytes of 6LoWPAN Adaptation Headers 33

34 FC DSN DSTPAN DST SRC Dispatch HC1 HC2 IPv6 UDP net Payload FCS FC DSN DSTPAN DST SRC Dispatch IPv6 UDP net Payload FCS 6LoWPAN Headers Full IPv6 Packet over with 64bit addressing 21 B 1 B 40 B 8 B 55 B 2 B Compressed IPv6 Packet over with 64bit addressing 21 B 3 B 97 B 2 B 1B 7 B 3B 34

35 Best-case HC1/HC2 compressed IPv6 Packet Dispatch HC1 header HC2 header LOWPAN_HC1 SAE DAE C NH 1 S D L Non Compre. data Hop Limit S_Port D_Port Checksum UDP Data. 35

36 Is Stateless Header Compression Enough? Stateless header compression for IPv6 packets (LOWPAN_HC1 & LOWPAN_HC2) -> reduce relatively large IPv6 and UDP headers down to few bytes Most effective for link local unicast communication Limitations of HC1 & HC2 Link local communications are mainly used for local protocols (neigbor discovery, DHCPv6, etc) within a LoWPAN network. Application layer protocols use global IPv6 addresses - HC1 should carry 64 bit prefix when using global addresses - HC1 should carry 128 bits address when using multicast communication - IPv6 next headers cannot be encoded efficiently 36

37 Context-based Header Compression Enhancements to HC1 & HC2 Hop limit (either 1 or 64) Compression of IPv6 next header fields (LOWPAN_NHC), e.g. IPv6-in-IPv6 tunneling Compression of UDP checksum Compression Format for IPv6 Datagrams in Low Power and Lossy Networks(6LoWPAN) RFC6282 Enables compression of global addresses Adds an additional context, when joining the LoWPAN. Context should be synchronized between compressor and decompressor 37

38 6LoWPAN IPHC Base Encoding TF NH HLIM CID SAC SAM M DAC DAM IPHC base header TF: Traffic Class, Flow Label: 00: ECN + DSCP + 4-bit Pad + Flow Label (4 bytes) 01: ECN + 2-bit Pad + Flow Label (3 bytes), DSCP is elided 10: ECN + DSCP (1 byte), Flow Label is elided 11: Traffic Class and Flow Label are elided. CID: Context Identifier Extension: 0: No additional 8-bit Context Identifier Extension is used. If context-based compression is specified in either SAC or DAC, context 0 is used. 1: An additional 8-bit Context Identifier Extension field immediately follows the DAM field. NH: Next Header: 0: Full 8 bits for Next Header are carried in-line. 1: The Next Header field is compressed and the next header is encoded using LOWPAN_NHC HLIM: Hop Limit: 00: The Hop Limit field is carried in-line. 01: The Hop Limit field is compressed and the hop limit is 1. 10: The Hop Limit field is compressed and the hop limit is : The Hop Limit field is compressed and the hop limit is 255. SAC: Source Address Compression 0: Source address compression uses stateless compression. 1: Source address compression uses stateful, contextbased compression. 38

39 6LoWPAN IPHC Base Encoding : TF Field TF = ECN DSCP - Flow Label TF = ECN Flow Label TF = 10 TF = TF: Traffic Class, Flow Label: ECN DSCP 00: ECN + DSCP + 4-bit Pad + Flow Label (4 bytes) : ECN + 2-bit Pad + Flow Label (3 bytes), DSCP is elided No bits 10: ECN + DSCP (1 byte), Flow Label is elided 11: Traffic Class and Flow Label are elided. 39

40 SAC/SAM values in 6LoWPAN IPHC SAC: Source Address Compression, SAM: Source Address Mode: SAC SAM Inline bits Full address (inline), no compression First 64 bit is elided (FE80:0:0:0:xxxx:xxxx:xxxx:xxxx) First 112 bit are elided (FE80:0:0:0:0000:00FF:FE00:XXXX) bit are elided (LL address is derived from MAC header) Unspecified address bit network prefix from the context + 64bit IID sent inline bit from the context + 16 bit short address sent inline bit address from the context DAC (Destination Address Compression) and DAM (Destination Address Mode) operations also similar: 40

41 Exchanage of Context Information 6LoWPAN Context Option (6CO) defined in draft-ietf-6lowpan-nd Type Length Context Length Res C CID Reserved Valid Lifetime... Context Prefix... 6LoWPAN Context Identifier Option (CID) defined in draft-ietf-6lowpan-hc-15 IPHC base header TF N HL C S SAM M D DAM SCI DCI..net. headers CID Extension 41

42 Introduction to Neighbor Discovery used in 6LOWPAN 42

43 IPv6 Neighbor Discovery Standard ND for IPv6 (RFC 4861 ND) assumes: A single link for an IPv6 subnet prefix Nodes are always on Heavy use of multicast traffic Image Source: ND: Neighbor Discovery NS: Neighbor Solicitation NA: Neighbor Advertisement DAD: Duplicate Address Detection 43

44 IPv6 vs 6LoWPAN Neighbor Discovery IPv6 ND (RFC 4861) Mulicast 6LoWPAN ND (draft-ietf-6lowpan-nd-18) - Unicast ND: Neighbor Discovery NS: Neighbor Solicitation NA: Neighbor Advertisement DAD: Duplicate Address Detection SLLAO: Source Link Layer Address Option PIO: Prefix Information Option ARO: Address Registration Option 6CO: 6LoWPAN Context Option ABRO: Authorative Border Router Option 44

45 6LoWPAN Neighbor Discovery Elimination of multicast-based address resolution for hosts. A host address registration feature using a new option in unicast Neighbor Solicitation and Neighbor Advertisement messages Host-initiated interactions to allow for sleeping hosts. It removes the need for periodic or unsolicited Router Advertisements from routers to hosts A new Neighbor Discovery option to distribute 6LoWPAN header compression context to hosts (6CO 6LoWPAN Context Option) No Duplicate Address Detection (DAD) is performed if EUI-64 based IPv6 addresses are used (as these addresses are assumed to be globally unique). DAD is optional if DHCPv6 is used to assign addresses Optional multihop duplicate address detection which uses two new ICMPv6 message types (DAR and DAC messages) 45

46 6LoWPAN Duplicate Address Detection DAR: Duplicate Address Registration DAC: Duplicate Address Confirmation 46

47 Fragmentation in 6LoWPAN 47

48 6LoWPAN Fragmentation IP packets are too large to fit in a frame are fragmented into multiple frames Network Packet V TC FL L NH HL 8 B Multiple Link Packets Src IP Dest IP 16 B 16 B net payload 15.4 MAC Fn IP FCS 15.4 MAC F2 IP FCS 15.4 MAC F1 IP FCS 48

49 Fragmentation All fragments of an IP packet carry the same tag Assigned sequentially at source of fragmentation Each specifies tag, size, and position Do not have to arrive in order Time limit for entire set of fragments First fragment Header Type = datagram_size datagram_tag Subsequent fragments - Header Type = datagram_size datagram_tag datagram_offset

50 Reassembly of Fragmented Packets The recipient of link fragments uses the following to rebuild whole packet sender's source address the destination's address datagram_size datagram_tag 50

51 Summary: 6LoWPAN Features Addressing: supports for e.g. 64-bit and 16-bit addressing Efficient header compression IPv6 base and extension headers, UDP header Useful with low-power link layers such as IEEE , narrowband ISM and power-line communications Optimized neighbour discovery protocol Unicast, multicast and broadcast support Multicast is compressed and mapped to broadcast Fragmentation 1280 byte IPv6 MTU -> 127 byte frames Support for IP routing (e.g. IETF RPL) Support for use of link-layer mesh (e.g ) IPv6-LoWPAN Router Stack Image Source: 51

52 6LoWPAN Operations to Start Functioning In order for a 6LoWPAN network to start functioning: 1. Link-layer connectivity between nodes (commissioning) Compatible physical and link-layer settings (modulation, channel, addressing, security, etc..) 2. Network layer address configuration, discovery of neighbors, registrations (bootstrapping) 3. Routing algorithm sets up paths (route initialization) 4. Continuous maintenance of

53 Hardware and Simulation Tools used 53

54 Hardware Platforms TelosB/TmoteSky: TI MSP430 + CC2420 Mica family: Atmel AVR + CC1000 imote2: Intel Xscale + CC2420 SunSpot: ARM920T + CC2420 Sensinode Zolertia Meshnetics... More on: [Image Source: The Sensor Network Museum] 54

55 Radio Chips TI/ChipCon CC2420 Atmel RF230 Ember Jennic... 55

56 Operating Systems for WSNs Well, more than just an OS: Applications Drivers for Chips, Sensors Development Environment, Compiler, Bootstrap Loader, Debugger Simulation Tools TinyOS nesc (Network Embedded Systems C) Atmel, MSP430,... Contiki C C64, Atari, Atmel, MSP430,... VM images available 56

57 Simulation Tools TOSSIM Shared Library of the OS & application, C/Python simulation scripts Event-based simulation Cooja/MSPsim Java with Contiki applications More: (Outdated) 57

58 Acknowledgement Some content and figures on these slides are taken from under the Creative Commons Attribution- Noncommercial-Share Alike 3.0 Unported License. To view a copy of this license, visit 58